Polymeric sheetings have been used to produce signage articles that have retroreflective capabilities. An article possesses a retroreflective capability when it can return a substantial portion of incident light in the direction from which the light originated. Retroreflectivity renders enhanced conspicuity to the article in low or restricted lighting situations, or in situations where sheeting materials must be viewed from a distance.
Polymeric sheetings also have been used to produce signage articles that have good durability. Durability of a signage article may be important in situations where the article may be exposed to harsh vapors, ultraviolet light, temperature or humidity extremes, and the like. Abrasion resistance and resistance to cleaning agents and the solvents used in cleaning solutions also are, in some cases, important aspects of durability. If extended useful life is not an important consideration (such as labels for rapid turnover packaging), lower cost non-extended life sheetings may be used.
Polymeric sheetings also have been used to form signage articles having indicia such as alphanumeric characters, bar codes, or graphics. Frequently, the signage articles will carry information that is repeated or incrementally varied over a large number of items; for instance, license plate validation stickers may have state or county identifying information repeated on a large number of validation stickers.
For many years, validation stickers have been applied to motor vehicles to indicate that applicable taxes have been paid and/or required registrations and inspections have been completed. In a common application, small stickers (typically on the order of about 2.5 by 3.8 centimeters or so (1 by 1.5 inches) and sometimes colloquially referred to as “tabs”) are applied to a designated location on the vehicle's license plate(s) to indicate that annual licensing taxes and registration fees have been paid. Other illustrative examples include application of stickers as proof of satisfactory vehicle safety inspections, satisfactory vehicle emission control inspections, and insurance coverage.
Products such as validation stickers are currently made by printing information on top of retroreflective sheeting using printing techniques such as letter press, offset press, screen printing, etc., that are typically not suitable for printing small quantities, for example. These types of printing processes normally provide satisfactory print quality, legibility, and adhesion; however, the equipment for these processes can be relatively expensive. In addition, when using letter press and offset press printing, print plates or rubber blankets must be prepared, and when using screen printing, a screen, must be prepared. The preparation of the plates, blankets, or screens, can be a costly, time-consuming process. Furthermore, in many cases, a solvent-borne colorant is used, which requires disposing of the solvent in an environmentally sound manner. Known processes also may necessitate the use of drying ovens and may require a certain amount of drying time. Further, the known means of printing indicia on articles are limited by the ease (or lack thereof) with which the information on individual items can be varied.
As laser printers, which use electrophotography, become less expensive, they are being used for printing on-demand and in small quantities. It would be desirable for validation stickers, and other signage articles that use polymeric sheeting, to be printed in small quantities and on-demand, for example. Unfortunately, however, conventional combinations of base polymeric sheeting and marking materials, e.g., those used in letter press and screen printing, are not generally sufficiently compatible to provide the desired adhesion, transparency, and durability under extremes in temperature, abrasive conditions, and exposure to chemicals (e.g., gasoline). Thus, the marking materials, e.g., toners, do not always adhere well to the base sheeting and the images formed by these marking materials are easily removed. This is a particular problem for validation stickers since they can be easily contacted by harsh chemicals, such as gasoline.
There are a variety of methods used to enhance adhesion of marking materials to sheeting material. For example, materials such as polyvinyl chloride, crosslinked polyurethane, and a composition that includes polyethylene terephthalate and a vinylidine/acrylonitrile copolymer have been used as the topmost layer of retroreflective sheeting to promote adhesion of marking materials coated thereon. Also, a halogen-free acrylic urethane topmost layer has been primed with a diluted solution of an acrylate polymer or adhesive, or corona treated to promote adhesion of marking materials. Clear coats of aliphatic or aromatic polyurethanes and acrylic polymers over the indicia have also been used to protect the underlying material, as have extruded thermoplastic cover films of aliphatic urethanes, copolymers of ethylene or propylene, and homopolymers of ethylene or propylene. Many of these, however, do not provide the necessary durability needed for many applications, particularly validation stickers that are easily contacted by harsh chemicals, such as gasoline.